Means and method for controlling the strength of acid in an alkylation unit

ABSTRACT

The strength of acid in an alkylation unit is controlled by a system using a signal corresponding to the anticipated demand on the acid by the reaction of olefin and isoparaffin in the presence of the acid. The reaction weakens the acid so that it is necessary to replace some of the weakened acid with fresh acid to maintain a desired acid strength. The control system includes apparatus sampling the olefin and isoparaffin entering the alkylation unit which provides a signal corresponding to the percent volume of acid degrading constituents formed during alkylation. A water analyzer samples the olefin and isoparaffin and provides a signal corresponding to their water content. Signals corresponding to sensed flow rates of fresh and discharged acid entering and leaving, respectively, the alkylation unit and of the olefin and isoparaffin are provided by sensors. A control circuit using analog computers develop the control signal in accordance with the signals from the sensors, the volume signal and the signal from the analyzer and equations hereinafter disclosed. The control signal is applied to a flow recorder controller which controls the flow rate of the fresh acid entering the alkylation unit so as to maintain the desired acid strength.

Child ct al.

May is, 1973 MEANS AND METHOD FOR CONTROLLING THE STRENGTH OF ACID IN AN ALKYLATION UNIT Filed:

Assignee:

Inventors: Edward T. Child, Hacienda Heights,

Calif; John E. May, Nederland, Tex.; William D. Stepanek, Fishkill,

Texaco Inc., New York, N.Y.

Aug. 5, 1971 Appl. No.: 169,385

Primary ExaminerEugene G. Botz Attorney-Thomas 1-1. Whaley and Carl G. Ries [57] ABSTRACT The strength of acid in an alkylation unit is controlled by a system using a signal corresponding to the anticipated demand on the acid by the reaction of olefin and isoparaffin in the presence of the acid. The reaction weakens the acid so that it is necessary to replace some of the weakened acid with fresh acid to maintain a desired acid strength. The control system includes apparatus sampling the olefin and isoparaffin entering the alkylation unit which provides a signal corresponding to the percent volume of acid degrading constituents formed during alkylation. A water analyzer samples the olefin and isoparaffin and provides a signal corresponding to their water content. Signals corresponding to sensed flow rates of fresh and discharged acid entering and leaving, respectively, the alkylation unit and of the olefin and isoparaffin are provided by sensors. A control circuit using analog computers develop the control signal in accordance with the signals from the sensors, the volume signal and the signal from the analyzer and equations hereinafter disclosed. The control signal is applied to a flow recorder controller which controls the flow rate of the fresh acid entering the alkylation unit so as to maintain the desired acid strength.

4 Claims, 11 Drawing Figures HYDROCARBON fi PRODUCT 27 2- ACID j SETTLER so FLOW RECORDER CONTROLLER FRElj ACID '7 CONTACTOR 0 /E20 29 FLOW RECORDER CONTROLLER 30 J35 lzg DISCHARGE ACID p WATER (E1 ONTROL ANALYZER MEANS PROGRAMMER /E7 /VA CHROMATOGRAPH QEE A A 0.0

MEANS v LTAGE MEANS SOURCE [44 B o 42 l OLEFIN 8.

ISOPARAFFIN PATENTH] RAY I 51375 SHEET 1 BF 6 FIG. I

I HYDROCARBON PRODUCT 27 I2- ACID j sETTLER 80) /8 FLOW RECORDER CONTROLLER CONTACTOR Z 0 29 FLOW RECORDER -fi- CONTROLLER (35 DISCHARGE ACID I WATER ANALYZER 'I P I L36 3? K PROGRAMMER 4 /E7 /VA 4o EA'EJ 5 OLEFIN DC. CHRONg AEF SAP SIGNAL VOLTAGE MEANS SOURCE M4 B' O 43 OLEFIN a ELTBBATB PATENTEDMAY 1 515375 SHEET 2 BF 6 R E M M A R G O R P it w PATENTEDHAY 1 51m SHEET 3 BF 6 3o: wiwzw PATENTED 3.733,473

sum u [1F 6 v p P MO m AW% 8 BOB 3 0 /m 7 l 1.555 4 A. E E 3 L D m w m 3 m m f m l 7 A I E M .rkJO m S 6 E 4 m E 3. w M a m f a fi m f j n 9 4 I m s F w UIL X 1/4 fi S 6 w u mm M 1 M X B X UM H s m I L .5... 5;... H U 4 5 6 4 7 9 M E 3 2 2 M V W W v v E E B V E A D! c I COMP.

I40 i i ISO SAMPLE 8| HOLD HG. E i

MEANS AND METHOD FOR CONTROLLING THE STRENGTH OF ACID IN AN ALKYLATION UNIT BACKGROUND OF THE INVENTION FIELD OF THE INVENTION The present invention relates to alkylation units in general and, more particularly, to a control system for an alkylation unit.

SUMMARY OF THE INVENTION A control system controls the strength of acid in an alkylation unit so as to maintain the acids strength at a predetermined level. The alkylation unit reacts an isoparaffin with olefin in the presence of the acid to provide an acid-hydrocarbon mixture to a settler where the hydrocarbon is separated from the acid to provide a hydrocarbon product. A portion of the acid is recycled while the remaining acid is discharged from the alkylation unit. Fresh acid is added to the recycled acid to affect the strength of the acid. The control system includes apparatus for controlling the strength of the acid in accordance with a control signal. A water analyzer samples the olefin and isoparaffin to provide a signal corresponding to the water content of the olefin and isoparaffin. A network samples the olefin and isoparaffin and provides a signal corresponding to the composition of the olefin. The flow rates of the olefin and isoparafiin, the fresh acid and the discharge acid are sensed by flow sensors which provide corresponding signals. A control circuit develops the control signal in accordance with the signals from the analyzer, the composition determining circuit and the sensors.

One object of the present invention is to control the strength of acid in an alkylation unit by determining the demand that will be made on the acid durinc an alkylation process which reacts olefins with an isoparaffin in the presence of acid.

Another object of the present invention is to sense the composition of an olefin prior to being reacted with an isoparaff'm in the presence of acid to determine the quantity of acid degrading compounds formed during alkylation.

The foregoing and other objects and advantages of the invention will appear more fully hereinafter from a consideration of the detailed description which follows, taken together with the accompanying drawings wherein one embodiment of the invention is illustrated by way of example. It is to be expressly understood, however, that the drawings are for illustration purposes only and are not to be construed as defining the limits of the invention.

DESCRIPTION OF THE DRAWINGS FIG. 6 is a diagrammatic representation of the reaction of an olefin and an isoparaffin in the presence of acid.

FIGS. 7 through 11 are detailed block diagrams of the V computer, the A computer, the B computer, the C computer and the M computer, respectively, shown in FIG. 1.

DESCRIPTION OF THE INVENTION Referring to FIG. 1, there is shown a portion of an alkylation unit in which an olefin is reacted with isoparaffin in the presence of a catalyst, such as sulfuric or hydrofluoric acid, to form a higher molecular weight isoparaffin. For purpose of explanation, the acid in the following description shall be sulfuric acid. The olefin may be butylene, propylene or a mixture of butylene and propylene, while the isoparaffin may be isobutane. The control system shown in FIG. 1 anticipates changes in the acid strength due to changes in the quantities of acid degrading compounds formed during alkylation to control the acid strength accordingly so as to speed up the control process.

The charge olefin and isoparaffin enters a contactor 4, by way of a line 6, where the charge olefin and isoparaffin are contacted with acid entering by way of a line 7. Contactor 4 provides an acid-hydrocarbon mix by way of a line 8 to an acid settler 12. Settler 12 separates the hydrocarbon product from the acid and the hydrocarbon product is discharged through a line 14 while the acid is removed by way of a line 16. Acid settler 12 may be the only acid settler in the alkylation unit or it may be the last acid settler of a group of acid settlers. Fresh acid enters line 16 by way of a line 17 as needed to maintain a desired acid strength. A pump 20 pumps the acid from line 16 into line 7. A portion of the acid in line 7 is discharged by way of a line 21. The discharge acid may be provided to another alkylation unit or disposed of.

The level in acid settler 12 is maintained by a conventional level sensor 27, a level recorder controller 28, a flow sensor 29 and a valve 30. Sensor 27 provides a signal to flow recorder controller 28 corresponding to the sensed acid level in settler 12. Flow sensor 29 and valve 30 are located in line 21. Sensor 29 provides signal E to flow recorder controller 28 corresponding to the discharge acid flow rate. The set point of controller 28 is adjusted by the signal from level sensor 27. When the acid level in settler 12 is high, the set point of flow recorder controller is adjusted by the signal from sensor 27 for an increased discharge acid flow rate. Controller 28 provides a signal to valve 30 causing it to pass more discharge acid until the sensed flow rate in line 21 corresponds to the target flow rate determined by the set point position of controller 28. By increasing the flow rate of the discharge acid while maintaining the fresh acid flow rate, the acid level in acid settler 12 decreases. Conversely, when the acid in level settler 12 is low, sensor 27 and controller 28 control valve 30 to decrease the discharge acid flow rate thereby increasing the acid level in acid settler 12.

A water analyzer 35 senses the water content of the olefin and isoparafiin in line 6 and provides a corresponding signal E Analyzer 35 may be of the type manufactured by Panarnetrics Inc. as their part No. 1000. Signal E, is applied to control means 36 which also receives a signal E corresponding to the flow rate of the olefin and isoparaffin in line 6 from a sensor 37.

Chromatograph means 40, which may be of the type manufactured by Bendix-Greenbriar Co. as their part No. C-l18, provides signals 13., and E Signal E is a pulse signal whose pulses coincide with the peaks of signal E; which corresponds to the composition of the olefin and isoparaffin. Pulse signal E. is applied to a programmer 41 which provides control pulses E through E to olefin signal means 44. Programmer 41 also receives a direct current voltage V from a source 45 of direct current voltages.

Programmer 41, which is shown in detail in FIG. 2, includes a manually-operable switch 50 which controls the starting and the stopping of the control operation. When closed, switch 50 passes direct current voltage V to an AND gate 51 which enables AND gate 51 along with a high level direct current output from a logic decoder 52. When open, switch 50 blocks voltage V A thereby disabling AND gate 51. AND gate 51 controls the counting by a counter 55 of pulses in pulse signal E.,. AND gate 51 when enabled passes pulse signal E to counter 55 and blocks pulse signal B, when disabled. Counter 55 provides a plurality of outputs to decoder 52. Decoder 52 includes a plurality of AND gates receiving the outputs from counter 55, each AND gate providing an output when a particular count is reached so that decoder 52 provides a plurality of outputs corresponding to different counts in counter 55.

When the number of pulses of pulse signal E equals the number of peaks to be sampled and held, decoder 52 provides a low level direct current output to AND gate 51 thereby disabling AND gate 51 to prevent further counting by counter 55, until counter 55 is reset by a reset pulse E A plurality of monostable multivibrators 57 provides pulse voltages E through E Each multivibrator of multivibrators 57 is triggered by a different output from decoder 56 to provide a pulse voltage which coincides with a different peak in signal E Pulse voltages E and E J are shown in FIGS. 3A and 38, respectively. The breaks in FIGS. 3A, 3B signify a break in time during which pulse voltages E through E, occur. The trailing edge of pulse voltage E, triggers a monostable multivibrator 60 to provide a pulse voltage E The trailing edge of pulse voltage E triggers a monostable multivibrator 60A causing multivibrator 60A to provide a pulse voltage E Pulse voltage E triggers multivibrator 608 which operates as a time delay to provide a pulse to multivibrator 60C. The width of the pulse from multivibrator 60B is such as to allow sufficient time for the operation of the analog computers. Multivibrator 60C provides reset pulse E which resets counter 55 so that the control operation may be recycled again.

Referring to FIG. 4, there is shown in detail, olefin signal means 44 providing a signal E,, which corresponds to the percent volume of acid consuming constituents in the olefin, to control means 36. Signal E from chromatograph means 40 is applied to sample and hold circuits 63 through 631. Pulses E through E, from programmer 41 control sample and hold circuits 63 through 63I, respectively, to hold different peaks of signal E The following Table relates a particular sample and hold circuit to a corresponding constituent.

Circuit Constituent Circuit Constituent 63 Ethane 6315 Normal Pentane 63A Propane 63F Propylene 63B Iso-Butane 63G Butylene 63C Normal Butane 63H Pentylene 63D lso-Pentane 631 All compounds with six or more carbon atoms The outputs from sample and hold circuits 63 through 631 are applied to multipliers 64 through 64I, respectively, where they are multiplied with direct current voltages V through V which correspond to various chromatograph means 40 scaling factors pertaining to the particular constituents. By way of example, voltages V through V may correspond to 0.02, 0.2, 1.0, 0.2, 0.15, 0.02, 0.2, 0.1, 0.02 and 0.1 volts, respectively.

Sample and hold circuits 65 through 651 are controlled by pulse E from programmer 41 to sample and hold the outputs from multipliers 64 through 641. Summing means 69 sums all of the outputs from sample and hold circuits 65 through 651 to provide a signal to dividers 70 through 70C. Dividers 70 through 70C also receive the outputs from sample and hold circuits 65F through 651, respectively and divide those outputs by the signal from summing means 69 to effectively normalize the outputs corresponding to the acid degrading constituents of the olefin. The signals from dividers 70 through 70C are sample and held by sample and hold circuits 71 through 71C, respectively, in response to pulse E, from programmer 41. The outputs from sample and hold circuits 71 through 71C are multiplied with direct current voltages V,, through V which correspond to ratios of pounds of acid consumed per gal lon of olefin for the acid consuming constituents, by multipliers 75 through 75C, respectively. Summing means 76 sums the outputs of multipliers 75 through 75C to provide signal E to control means 36.

Control means 36 as shown in detail in FIG. 5 develops a control signal E which is used to control the fresh acid entering the alkylation unit. Control E subtracted from a direct current voltage V provided by source 43, which corresponds to a predetermined target acid strength, by subtracting means 79. Subtracting means 79 provides an error signal E to a conventional type flow recorder controller 80 which receives a signal E from a sensor 81 in line 17. Signal E adjusts the set points of controller 80. Signal E corresponds to the flow rate of the fresh acid entering the alkylation unit. Controller 80 controls a valve 83 to regulate the fresh acid flow rate in accordance with the difference between the sensed flow rate signal E and the desired flow rate as determined by the set points positions. Control means 36 develops signal E in accordance with signals E E E and E direct current voltages V through V V through V and V 'and the following equations:

pB E

4. -owl 5. Wt. acid and where A, B, C are quantities of three compounds 0? curring within contactor 4, i.e. the first compound results from an ultimate reaction of the olefin with the isoparaffin to form an alkylate, the second compound is an acid contaminate which is formed from a reversible reaction with the first compound, and the third compound is an acid contaminate resulting from an in reversible reaction with the first compound. The second and third compounds remaining in the acid in line 16, respectively, M is the water in the acid phase and the olefin and isobutane in line 6; R R R and R are reaction rates constants which are predetermined from a laboratory analysis of the reaction of the olefin with the isobutane in the presence of the acid. A math model is shown in FIG. 6 from which equations 1 through 6 were obtained; V and V, are the initial volume and the present volume, respectively, of acid phase in c.c.; p p,,, p,,, p and p are the densities of the acid in the contactor 4, the three compounds and water, respectively; W W W and W are the molecular weight of the three compounds and water, respectively, F corresponds to the fresh acid flow rate and F, corresponds to the discharge acid flow rate. Values for WA W8 0, M ps. PA, PE. pc and PM y be predetermined from laboratory analysis of the olefin, the isobutane and the acid, while the density p and the molecular weight W of the water are known.

Referring to FIG. 5, variable resistors 87, 88 reduce signal E to provide signals E E which correspond to the terms F and 'y,,,, respectively, in the aforementioned equations, having units of grams/sec and moles of water in the fresh acid per second. Signal E is conditioned by a variable resistor 89 to provide a signal E which corresponds to the term F, in equation 6 having units of gms/sec.

A V, computer 90 receives signals E E from resistors 87 and 89, respectively, control pulses E from a pulse generator 91, direct current voltages V through V from source 43, and signals E E E and E The development of signals E E E and E which correspond to the M, A, B and C terms in the aforementioned equation, will be hereinafter disclosed. Multivibrator 94 is triggered by the trailing edge of each control pulse E to provide a pulse E so that a pulse E immediately precedes each pulse E Computer 90 provides a signal E corresponding to the present volume V, of the acid phase in accordance with the received signals and voltages, and equation 6. Referring to FIGS. and 7, voltages V through V are multiplied with signals E through E respectively by multipliers 95 through 95C, respectively. Voltages V V V and V correspond to the predetermined ratios of molecular weight to density W /p W Ap W /p and W /p of the three compounds and the water in the acid phase, respectively; while signals E E E and E correspond to the terms M, A, B and C, respectively. Subtracting means 96 subtracts signal E from signal E to provide an output, corresponding to the term (Fpin equation 6, to an integrator 100.

A sample and hold circuit 101 samples and holds the output of integrator 100 just prior to pulse E Pulses E control integrator 100 causing integrator 100 output to go to zero when a timing pulse E occurs. The

output from sample and hold circuit 101 corresponds to the integral A multiplier 102 multiplies the output from sample and hold circuit 101 with voltage V which corresponds to the reciprocal Up, of the density of the acid to provide an output corresponding to the term in equation 6. Summing means 103 sums the outputs from multipliers through 95C and 101 with voltage V,,, which corresponds to the initial volume V to provide signal E Referring again to FIG. 5, a multiplier 108 multiplies voltage V from source 43 with signal E from resistor 89 to provide a signal corresponding to F ,/P,V in the aforementioned equations. Signals E and E are multiplied together by a multiplier 110 whose output is reduced by a variable resistor 114 to provide a signal E corresponding to the term a in equation 1. Resistor 1 14 is used so as to conform units of measurement, the term ar is in gms/sec.

An A computer 115 provides signal E in accordance with signals E E E and E direct current voltages V through V from source 43 and equation 1. Referring now to FIG. 5 and 8 voltages V through V which correspond to the terms R R and R respectively, are summed along with signal E by summing means 116 to provide a signal corresponding to the quantity (R R R, F,,/ ,V, A multiplier 1 l8 multiplies the output from summing means 116 with signal E which corresponds to the term A. Another multiplier 119 multiplies direct current voltage V which corresponds to the term R with signal E which corresponds to the term B, to provide a signal which is summed with signal E by summing means 120. Subtracting means 124 subtracts the output provided by multiplier 118 from the output provided by summing means 120. The output from subtracting means 124 is operated upon by an integrator 125 and a sample and hold circuit 126 receiving pulses receiving pulses E and E respectively, to provide signal E which is also fed back to multiplier 118.

Referring to FIGS. 5 and 9, signal E which corresponds to the term B, is provided by a B computer 130 in accordance with direct current voltages V and V signals E and E and equation 2. Signal B is summed with direct current voltage V which corresponds to the term R by summing means 131 to provide a signal corresponding to R F /p V, which is multiplied with signal E by a multiplier 132. Another multiplier 133 multiplies signal E with voltage V to provide an output corresponding to the term R A. Subtracting means 138 subtracts the output provided by multiplier 132 from the output provided by multiplier 133. An integrator 139 and a sample and hold circuit 140, receiving pulses E and E respectively, operates on the output from subtracting means 138 to provide signal E which is also fed back to multiplier 132.

Signal E which corresponds to the term C in the aforementioned equations, is provided by a C computer 140 in accordance with signals E and E and direct current voltage V Referring to FIGS. 5 and 10, signal E is multiplied with voltage V by a multiplier 144 to provide a signal corresponding to the term R A. Another multiplier 145 multiplies signal E with signal E to provide an output corresponding to the term (F lp V,,)C. Subtracting means 148 subtracts the output provided by multiplier 145 from the output provided by multiplier 144. An integrator 150 and a sample and hold circuit 151, receiving pulses E and E respectively, operates on the output from subtracting means 148 to provide signal E which is also fedback to multiplier 145.

Referring back to FIG. 5, a multiplier 151 multiplies signals E E together and the resulting output is reduced by variable resistor 152 to provide a signal E corresponding to the term a,,,.

Signal B is provided by an M computer 155 in accordance with signals E E and E and equation 4. Referring now to FIG. 11, summing means 160 sums signals E and E to provide an output corresponding to the term a 'y Signal E is multiplied with signal E by a multiplier 161 to provide an output corresponding to the term (F,,/p V,,)M. Subtracting means 162 subtracts the output provided by multiplier 161 from the output provided by summing means 164} to provide a signal which is operated on by an integrator 165 and a sample and hold circuit 166, receiving pulses E and E respectively, to provide signal E Signal E is also fed back to multiplier 1611.

Referring back to FIG. 5, signals E E E and E from computers 115, 1311, 140 and 155, respectively, are multiplied with direct current voltages V through V respectively, by multipliers 170 through 170C. Voltages V through V correspond to the predetermined molecular weights of water and the first, second and third compounds, respectively. Summing means 171 sums the outputs of multipliers 170 through 170C. Direct current voltage V which corresponds to the term 1 in equation is divided by signal E by a divider 173. The output from divider 173 is multiplied with voltage V by a multiplier 174 to provide an output corresponding to the term l/p,,V,. Another multiplier 176 multiplies the same signal from summing means 171 with the signal from multiplier 174 and the resulting output is subtracted from voltage V by subtracting means 177 to provide control signal E A digital computer may be used instead of control means 36, programmer 41 and olefin signal means 44. Signals E E E E and E are converted to digital signals by conventional type analog to-digital converters and the digital signals are applied to the digital computer. The digital computer provides a digital control signal in accordance with the aforementioned equations. The digital control signal is then converted to analog signal E by a conventional type digital-to-analog converter.

The system of the present invention as heretofore described controls the strength of acid in an alkylation unit by determining the demand that will be made on the acid during the alkylation process. The alkylation process reacts an olefin with an isoparaffin in the presence of acid. The composition of the olefin is sensed and the quantity of acid consuming constituent of the olefin is determined from the sensed composition of the olefin.

What is claimed is:

l. A system for controlling the strength of an acid in an alkylation unit wherein an isoparaffin is reacted with olefin in the presence of the acid to provide an acidhydrocarbon mixture to a settler where the hydrocarbon is separated from the acid to provide a hydrocarbon product and a portion of the acid is recycled while the remaining acid is discharged from the alkylation unit, wherein fresh acid is added to the recycle acid to affect the strength of the acid and wherein the reaction of the olefin with the isoparaffin in the presence of the acid results in a first compound being formed from the olefin and isoparafiin in the acid phase and immediately leaving the acid phase after formation, a second compound being formed in the acid phase from the first compound and which may return to the first compound, and a third compound in the acid phase formed from the first compound and which cannot return to the first compound, comprising means for controlling the strength of the acid in accordance with a control signal, means forsensing the water content of the olefin and the isoparaffin and providing a signal corresponding thereto, means for determining the composition of the olefin and providing a corresponding composition signal, means for sensing the flow rate of the olefin and providing a signal corresponding thereto, means for sensing the flow rates of the fresh acid and the discharged acid and providing signals corresponding thereto, said control signal means includes a first circuit connected to the olefin and isoparaffin flow rate sensor and to the composition signal means provides a signal corresponding to the quantity d of acid consuming constituents contacting the acid; a second circuit connected to the analyzer and to the olefin and isoparaffin flow rate sensing means provides a signal corresponding to the quantity or, of water in the olefin and isoparaffin contacting the acid; means connected to the fresh acid flow rate sensing means for providing a signal corresponding to the quantity 'y,, of water in the fresh acid entering the alkylation unit; means for providing direct current voltages corresponding to the reaction rates R R R and R between the olefin, the isoparaffin, the acid, the first, second and third compounds, to the initial volume V, of acid in the alkylation unit, to the molecular weights W W and W of the first, second and third compounds, respectively, to the molecular weight W of water, to the densities p p and p of the first, second and third compounds, respectively, to the densities p,, and p of the acid and of water, respectively, and to a unit value 1; first analog computing means for providing signals corresponding to the quantities A, B and C of the first, second and third compounds, respectively, and to the quantity M of water in accordance with the a a and 7 signals and the discharged acid flow rate and the following equations:

T F f i ps s Pa e W M W C M dt and with the following equation:

Wt. acid/l= l.0 W M+ W A W B W C) 2. A system as described in claim 1 in which the determining means includes chromatograph means periodically sampling the olefin and isoparaffin for providing a first signal, whose amplitude peaks correspond to different constituents of the olefin and isoparaffin, and a pulse signal, each pulse in the pulse signal coincides with a different peak of the signal from the chromatograph means, program means connected to the chromatograph means and responsive to the pulse signal for providing control pulses, and means connected to the chromatograph means, to the control signal means and to the program means and controlled by the control pulses, for providing a signal which corresponds to the portion of the olefin that is acid consuming as the composition signal in accordance with the first signal from the chromatograph means.

3. A method for controlling the strength of an acid in an alkylation processing unit wherein an isoparaffin is reacted with olefin in the presence of the acid to provide an acid-hydrocarbon mixture to a settler where the hydrocarbon is separated from the acid to provide a hydrocarbon product and a portion of the acid is recycled while the remaining acid is discharged from the alkylation unit, wherein fresh acid is added to the recycle acid to affect the strength of the acid and wherein the reaction of olefin with isoparaffin in the presence of acid results in the first compound being formed from the olefin and isoparaffin in the acid phase and which leaves the acid phase upon formation, a second compound in the acid phase being formed from the first compound and which may return to the first compound, and a third compound in the acid phase formed from the first compound and which cannot return to the first compound, which comprises determining the composition of the olefin; sensing the flow rates of the olefin and isoparaffin, the fresh acid and the discharge acid; providing a signal corresponding to the quantity a of acid consuming constituents contacting the acid in accordance with the sensed olefin and isoparaffin flow rate and with the determination of the olefin composition; providing a signal corresponding to the quantity a, of water in the olefin and isoparaffin contacting the acid, providing a signal corresponding to the quantity 7, of water in the fresh acid entering the alkylation unit; providing direct current voltages corresponding to the reaction rates R R R and R between the olefin,

the isoparaffin, the acid, the first, second and third compounds, to the initial volume V of acid in the al kylation unit, to the molecular weights W W,, and W of the first, second and third compounds, respectively, to the molecular weight W of water, to the densities p p and p of the first, second and third compounds, respectively, the densities p, and p of acid and water, respectively, and to a unit value l; providing signals corresponding to the quantities A, B and C of the first, second and third compounds, respectively, formed during the reaction and to the quantity M of water in accordance with the d a and 7 signals and the discharged acid flow rate and the following equations:

where T is a predetermined time and providing a signal corresponding to the weight of the acid as the control signal in accordance with 1.0, W W W and voltages, the A, B, C, M and V, signals and the following equation:

Wt. acid/ 1.0 W M W A W B W C) /Pa a)- 4. A method as described in claim 3 in which the determination step includes sampling the olefin and isoparaff'm; providing a signal, whose amplitude peaks correspond to different constituents of the olefin and isoparaft'm; providing control pulses, each control pulse coinciding with a different peak of the last mentioned provided signal, and providing a signal which corresponds to the portion of the olefin that is acid consuming as the composition signal in accordance with the last mentioned provided signal. 

1. A system for controlling the strength of an acid in an alkylation unit wherein an isoparaffin is reacted with olefin in the presence of the acid to provide an acid-hydrocarbon mixture to a settler where the hydrocarbon is separated from the acid to provide a hydrocarbon product and a portion of the acid is recycled while the remaining acid is discharged from the alkylation unit, wherein fresh acid is added to the recycle acid to affect the strength of the acid and wherein the reaction of the olefin with the isoparaffin in the presence of the acid results in a first compound being formed from the olefin and isoparaffin in the acid phase and immediately leaving the acid phase after formation, a second compound being formed in the acid phase from the first compound and which may return to the first compound, and a third compound in the acid phase formed from the first compound and which cannot return to the first compound, comprising means for controlling the strength of the acid in accordance with a control signal, means for sensing the water content of the olefin and the isoparaffin and providing a signal corresponding thereto, means for determining the composition of the olefin and providing a cOrresponding composition signal, means for sensing the flow rate of the olefin and providing a signal corresponding thereto, means for sensing the flow rates of the fresh acid and the discharged acid and providing signals corresponding thereto, said control signal means includes a first circuit connected to the olefin and isoparaffin flow rate sensor and to the composition signal means provides a signal corresponding to the quantity Alpha o of acid consuming constituents contacting the acid; a second circuit connected to the analyzer and to the olefin and isoparaffin flow rate sensing means provides a signal corresponding to the quantity Alpha m of water in the olefin and isoparaffin contacting the acid; means connected to the fresh acid flow rate sensing means for providing a signal corresponding to the quantity gamma m of water in the fresh acid entering the alkylation unit; means for providing direct current voltages corresponding to the reaction rates R1, R2, R3 and R4 between the olefin, the isoparaffin, the acid, the first, second and third compounds, to the initial volume Vo of acid in the alkylation unit, to the molecular weights WA, WB and WC of the first, second and third compounds, respectively, to the molecular weight WM of water, to the densities Rho A, Rho B and Rho C of the first, second and third compounds, respectively, to the densities Rho s, and Rho M of the acid and of water, respectively, and to a unit value 1; first analog computing means for providing signals corresponding to the quantities A, B and C of the first, second and third compounds, respectively, and to the quantity M of water in accordance with the Alpha o, Alpha m and gamma m signals and the discharged acid flow rate and the following equations:
 2. A system as described in claim 1 in which the determining means includes chromatograph means periodically sampling the olefin and isoparaffin for providing a first signal, whose amplitude peaks correspond to different constituents of the olefin and isoparaffin, and a pulse signal, each pulse in the pulse signal coincides with a different peak of the signal from the chromatograph means, program means connected to the chromatograph means and responsive to the pulse signal for providing control pulses, and means connected to the chromatograph means, to the control signal means and to the program means and controlled by the control pulses, for providing a signal which corresponds to the portion of the olefin that is acid consuming as the composition signal in accordance with the first signal from the chromatograph means.
 3. A method for controlling the strength of an acid in an alkylation processing unit wherein an isoparaffin is reacted with olefin in the presence of the acid to provide an acid-hydrocarbon mixture to a settler where the hydrocarbon is separated from the acid to provide a hydrocarbon product and a portion of the acid is recycled while the remaining acid is discharged from the alkylation unit, wherein fresh acid is added to the recycle acid to affect the strength of the acid and wherein the reaction of olefin with isoparaffin in the presence of acid results in the first compound being formed from the olefin and isoparaffin in the acid phase and which leaves the acid phase upon formation, a second compound in the acid phase being formed from the first compound and which may return to the first compound, and a third compounD in the acid phase formed from the first compound and which cannot return to the first compound, which comprises determining the composition of the olefin; sensing the flow rates of the olefin and isoparaffin, the fresh acid and the discharge acid; providing a signal corresponding to the quantity Alpha o of acid consuming constituents contacting the acid in accordance with the sensed olefin and isoparaffin flow rate and with the determination of the olefin composition; providing a signal corresponding to the quantity Alpha m of water in the olefin and isoparaffin contacting the acid, providing a signal corresponding to the quantity gamma m of water in the fresh acid entering the alkylation unit; providing direct current voltages corresponding to the reaction rates R1, R2, R3 and R4 between the olefin, the isoparaffin, the acid, the first, second and third compounds, to the initial volume Vo of acid in the alkylation unit, to the molecular weights WA, WB and WC of the first, second and third compounds, respectively, to the molecular weight WM of water, to the densities Rho A, Rho B and Rho C of the first, second and third compounds, respectively, the densities Rho s and Rho M of acid and water, respectively, and to a unit value 1; providing signals corresponding to the quantities A, B and C of the first, second and third compounds, respectively, formed during the reaction and to the quantity M of water in accordance with the Alpha O, Alpha m and gamma m signals and the discharged acid flow rate and the following equations:
 4. A method as described in claim 3 in which the determination step includes sampling the olefin and isoparaffin; providing a signal, whose amplitude peaks correspond to different constituents of the olefin and isoparaffin; providing control pulses, each control pulse coinciding with a different peak of the last mentioned provided signal, and providing a signal which corresponds to the portion of the olefin that is acid consuming as the composition signal in accordance with the last mentioned provided signal. 